JP5541664B2 - Method for measuring band gap electronic properties of wide gap semiconductors - Google Patents

Description

The present invention relates to a method for measuring band gap electronic properties of a wide gap semiconductor.

In next-generation semiconductors for multi-function devices, band gap electronic properties are extremely important factors directly related to device characteristics, and measurement techniques are important. For example, Non-Patent Document 1 discloses a band gap electronic property measurement technique such as Si or GaAs that forms a Schottky electrode with a noble metal such as Pt on the surface of a semiconductor.

Simon M. Sze, "Physics of Semiconductor Devices" 2nd Edition, Chapter 5. "Metal-Semiconductor Contacts" (p.245-311), JohnWiley & Sons, 1981 (published simultaneously in Canada)

However, the technique of Patent Document 1 cannot sufficiently measure the band gap electronic properties of wide gap semiconductors such as GaN and ZnO. One of the reasons is that a good Schottky diode necessary for measuring physical properties cannot be produced. Generally, for highly sensitive electrical measurement, it is necessary to form a Schottky electrode with a noble metal having a large work function such as Pt. In this case, the semiconductor carrier concentration range in which measurement is possible is 1 × 10 ¹⁶ to There was a problem of being limited to 1 × 10 ¹⁷ cm ⁻³ .
In addition, in order to investigate the entire band gap of a wide gap semiconductor, it is considered that a measurement technique using photoexcitation can be suitably used. However, there is a problem that a noble metal Schottky electrode cannot enter light into the semiconductor. It was. In particular, when considering the practical application of the device, the film quality (point defect level) management heteroepitaxially grown on the Si substrate is extremely important, but it is not possible to irradiate light from the back like the epifilm on the sapphire substrate. Therefore, it is not possible to apply a measurement technique using photoexcitation. That is, it cannot be applied to devices and materials formed on industrially important Si semiconductor substrates.

Accordingly, an object of the present invention is to realize a method for measuring the band gap electronic properties of a wide gap semiconductor using photoexcitation.

In order to achieve the above object, according to the first aspect of the present invention, there is provided a band gap electronic property measurement method for a wide gap semiconductor, wherein the wide gap semiconductor and the Schottky junction are formed on the surface of the wide gap semiconductor. A Schottky electrode forming step of forming an organic metal film having translucency, and having a predetermined wavelength from the organic metal film side to the wide gap semiconductor on which the organic metal film is formed by monochromatic light irradiation means. A monochromatic light is irradiated at a predetermined timing and intensity, a pulse voltage of a predetermined voltage intensity is applied to the wide gap semiconductor formed with the organometallic film at a predetermined timing by a voltage pulse generating means, and the impedance measuring means The impedance of the wide gap semiconductor on which the organometallic film is formed is detected, and after the pulse voltage is applied Based on the impedance of the monochromatic light irradiation environment of constant wavelength, the wide by correspondence between the wavelength of the irradiated said monochromatic light, a capacitance or conductance change rate of the electron depletion layer formed immediately below the Schottky electrode A technical means for evaluating the band gap electronic properties of the gap semiconductor is used.

According to the first aspect of the present invention, the surface of the wide gap semiconductor to be measured in the Schottky electrode formation step has a light-transmitting property capable of forming a Schottky junction with the wide gap semiconductor, and has a wide band gap. A conductive organometallic film having an appropriate work function is formed as a Schottky electrode of a wide gap semiconductor, monochromatic light is irradiated from the organometallic film side by monochromatic light irradiation means, and an organometallic film is produced by voltage pulse generating means. A pulse voltage having a predetermined voltage intensity is applied to the wide gap semiconductor formed with a predetermined timing, and the impedance of the wide gap semiconductor on which the organometallic film is formed can be detected by the impedance measuring means.
Then, based on the impedance under the monochromatic light irradiation environment of a predetermined wavelength after applying the pulse voltage, the wavelength of the monochromatic light irradiated and the change rate of the capacitance or conductance of the electron depletion layer formed immediately below the Schottky electrode Based on the correspondence, the transient response characteristics of capacitance or conductance according to optical excitation such as deep level and valence band information are obtained, and band gap electronic property measurement such as deep level and valence band information of wide gap semiconductor is performed. It can be performed with high sensitivity.
Since the work function of the organic metal film is larger than that of the noble metal, band gap electronic property measurement is possible even in a wide gap semiconductor having a high carrier concentration of about 1 × 10 ¹⁸ cm ⁻³ . Thereby, the band structure analysis of a wide gap semiconductor within a wide carrier concentration range of 1 × 10 ¹⁶ to 1 × 10 ¹⁸ cm ⁻³ becomes possible. Since it is possible to measure a high carrier concentration, it is possible to detect the band gap physical property information of the semiconductor surface portion, which was difficult to measure with the prior art.
Measurements are made by irradiating monochromatic light from the organic metal film side by means of monochromatic light irradiation means, so it is possible to measure the electronic properties of various wide gap semiconductors grown on a substrate that does not allow light such as Si to pass through. It can be applied to various semiconductors regardless of the substrate type.

According to a second aspect of the present invention, in the method for measuring a band gap electronic property of a wide gap semiconductor according to the first aspect, the measurement frequency of the impedance is set to a frequency equal to or higher than a cutoff frequency of the organometallic film. Use appropriate means.

According to the second aspect of the present invention, since the impedance measurement frequency is set to a frequency equal to or higher than the cutoff frequency of the organometallic film, the influence of dielectric dispersion can be avoided and the measurement accuracy can be improved. it can.

According to a third aspect of the present invention, in the method for measuring a band gap electronic property of a wide gap semiconductor according to the first or second aspect, the change rate of the capacitance is used for evaluating the band gap electronic physical property of the wide gap semiconductor. In this case, a technical means is used in which the change rate of the capacitance is measured by changing the measurement frequency of the impedance, the measurement condition is set based on the measurement frequency dependency, and the in-band gap level information is evaluated.

In the method for measuring the band gap electronic properties of the wide gap semiconductor according to the present invention, the change rate of the capacitance is measured by changing the impedance measurement frequency, and the dependency on the measurement frequency is examined, as in the third aspect of the invention. Thus, it is possible to set the measurement frequency at which the in-band gap level information is appropriately obtained and evaluate the in-band gap level information.

According to a fourth aspect of the present invention, in the method for measuring a band gap electronic property of the wide gap semiconductor according to the first or second aspect, the change rate of the capacitance is used for evaluating the band gap electronic physical property of the wide gap semiconductor. In this case, a technical means is used in which the change rate of the capacitance is measured by changing the measurement voltage, the measurement condition is set based on the measurement voltage dependency, and the band gap level information of the surface layer is evaluated.

In the method of measuring the band gap electronic properties of the wide gap semiconductor according to the present invention, the change rate of the capacitance is measured by changing the measurement voltage and the dependence on the measurement voltage is examined, as in the invention of claim 4. It is possible to set the measurement voltage at which the band gap level information of the layer can be appropriately obtained and evaluate the band gap level information of the surface layer.

It is explanatory drawing which shows the structure of the evaluation sample provided with the semiconductor material evaluated in this embodiment. FIG. 1A is a cross-sectional explanatory view of an evaluation sample, and FIG. 1B is a cross-sectional explanatory view of a state in which an organometallic film is formed on a semiconductor material of the evaluation sample. It is explanatory drawing which shows the voltage-current characteristic of the semiconductor material evaluated by this embodiment. It is explanatory drawing which shows the capacity | capacitance-current characteristic of the semiconductor material evaluated by this embodiment. It is explanatory drawing which shows the evaluation apparatus used by this invention. It is explanatory drawing which shows the measuring method of a band structure. It is a conceptual diagram of the band structure which can be measured by this invention. It is explanatory drawing which shows the measurement frequency dependence of a capacitance and admittance. It is explanatory drawing which shows the measurement frequency dependence of the spectrum which shows the relationship between incident light energy and the variation | change_quantity of a capacitance. It is explanatory drawing which shows the measurement voltage (depth area) dependence of the spectrum which shows the relationship between incident light energy and the variation | change_quantity of a capacitance.

Embodiments of the present invention will be described with reference to the drawings. The evaluation of the band gap electronic properties of a GaN thin film will be described as an example of the evaluation of the band gap electronic properties of a semiconductor.

First, a light-transmitting organometallic film for forming a semiconductor material and a Schottky diode is formed on a semiconductor thin film to be evaluated. In this embodiment, as shown in FIG. 1A, an evaluation sample formed by laminating an n-GaN film 13 on a c-Al ₂ O ₃ substrate 11 with a ud (undope) -GaN film 12 interposed therebetween. Prepare 1 On the n-GaN film 13, an ohmic metal electrode 14 made of In or the like is formed. Here, the n-GaN film 13 is a GaN film doped with Si at a carrier concentration of 6.3 × 10 ¹⁷ cm ⁻³ .

Next, as shown in FIG. 1B, a translucent organic metal that forms a high Schottky barrier exceeding 1.2 eV with the n-GaN film 13 on the n-GaN film 13, for example. An organometallic film 15 is formed by a polyaniline film (PANI) which is a film. The organic metal film 15 is formed, for example, by applying a polyaniline aqueous solution to the surface of the n-GaN film 13 by spin coating, baking at 150 ° C., and removing unnecessary portions. The thickness of the organic metal film 15 is formed, for example, to about 200 nm. The light transmittance of the organic metal film 15 produced in this way is 75 to 85% at a wavelength of 250 to 280 nm, 90% at a wavelength of 280 to 400 nm, and 90% in the visible light region, and is excellent in translucency.

When the current-voltage characteristics of the organic metal film 15 / n-GaN film 13 are evaluated, as shown in FIG. 2, the dark current-voltage characteristics by the semi-logarithmic display indicate the rectification characteristics, and the organic metal film 15 It was confirmed that a Schottky barrier was formed by the n-GaN film 13. That is, the metal organic film 15 and the n-GaN film 13 form a Schottky diode. Here, the diode ideal factor n was calculated as 1.2 and the Schottky barrier height φ ₀ was calculated as 1.2 eV by fitting in the linear region. Further, the rectification ratio was a good value of 1.8 × 10 ⁶ .

Further, when the capacitance when the reverse bias was applied to the electrode was measured to evaluate the capacitance-voltage characteristic, the capacitance-voltage characteristic showed a straight line relationship to the right as shown in FIG. Here, the donor concentration _{N D} is the slope of the linear region was calculated to 6.4 × ¹⁰ 17 ^{cm -3.} From the X-intercept, the built-in potential Vbi was calculated to be 1.12 eV, which was in good agreement with the Schottky barrier height φ ₀ obtained from FIG. Thereby, it was confirmed that a good Schottky diode was formed by the organic metal film 15 and the n-GaN film 13.

As an evaluation apparatus for an evaluation sample 1 as shown in FIG. 1B in which a light-transmitting organometallic film for forming a semiconductor material and a Schottky diode is formed on a semiconductor material, the inventor of the present invention An organic material evaluation apparatus described in Japanese Patent Application Laid-Open No. 2008-14668, which is partially developed, can be used.

As shown in FIG. 4, the evaluation device 2 includes a voltage pulse generation unit 21, an impedance measurement unit 22, a monochromatic light irradiation unit 23, and a control unit 24. The voltage pulse generator 21 applies a predetermined voltage pulse between the metal electrode 14 and the organometallic film 15. The impedance measuring unit 22 measures the impedance between the metal electrode 14 and the organometallic film 15 at a predetermined timing. The monochromatic light irradiation unit 23 irradiates the organic metal film 15 with light having a predetermined wavelength intensity at a predetermined timing.

The control unit 24 controls the voltage pulse generation unit 21, the impedance measurement unit 22, and the monochromatic light irradiation unit 23, and includes a condition setting unit / measurement control unit 25, a calculation unit 26, and the like.

The condition setting unit / measurement control unit 25 sets and controls the light irradiation timing, wavelength, and intensity for the monochromatic light irradiation unit 23, and the voltage pulse intensity (pulse voltage) and pulse period for the voltage pulse generation unit 21. The application timing is controlled, and the impedance measurement unit 22 is controlled with respect to the impedance measurement timing.

The calculation unit 26 collects the impedance values measured by the impedance measurement unit 22, obtains data such as irradiation light data (energy conversion value), voltage pulse application timing, and intensity, and calculates a correspondence relationship with the impedance. ·To detect.

The evaluation sample 1 is evaluated using the evaluation device 2. First, as shown in FIG. 5A, a zero bias or forward voltage pulse is applied between the metal electrode 14 and the organic metal film 15 for several microseconds to several tens of seconds with light blocked. Thus, charge injection is performed in the band gap level of the n-GaN film 13. Here, the anode is the organic metal film 15, and the cathode is the metal electrode 14. The voltage value, pulse width, etc. of the pulse can be set according to the charge injection property to the semiconductor material to be evaluated.

After applying the pulse voltage, the voltage applied to the metal electrode 14 and the organic metal film 15 is used as a measurement voltage, and monochromatic light having a predetermined wavelength is irradiated to the n-GaN film 13 for a certain period of time. When the n-GaN film 13 is irradiated with monochromatic light, a shallow level is thermally excited in a short time within the band gap as shown in FIG. 6, and then optical excitation occurs. This optical excitation includes excitation from a deep band gap level to be measured in the present embodiment.

The impedance measuring unit 22 measures the time response of the capacitance C of the n-GaN film 13 based on this thermal excitation and optical excitation as shown in FIG.

By the above measurement, the relationship (rate of change) of the ratio of capacitance to light irradiation with a predetermined wavelength can be obtained. As shown in FIG. 5 (B), by changing the wavelength of the monochromatic light to be irradiated from the low energy side to the high energy side and repeatedly measuring, the calculation unit 26 causes the energy and capacitance of the incident light to enter the organic material. A relationship with the rate of change can be obtained. As a result, the level in the band gap of the semiconductor material can be sequentially detected from the energy shallow direction to the deep direction.

According to the method for measuring the band gap electronic properties of a wide gap semiconductor according to the present invention, a translucent organometallic film capable of forming a Schottky junction with the wide gap semiconductor on the surface of the n-GaN film 13 which is a wide gap semiconductor. Is formed as a wide-gap semiconductor Schottky electrode, and the monochromatic light irradiating unit 23 produces a monochromatic color. As the light, for example, monochromatic light having sufficiently high wavelength resolution is spectrally irradiated from the side of the organic metal film 15, and the voltage pulse generator 21 applies a predetermined amount to the wide gap semiconductor n-GaN film 13 on which the organic metal film 15 is formed. A pulse voltage having a predetermined voltage intensity is applied at the timing, and the impedance measurement unit 22 applies the organic metal film 1. It is possible to detect the impedance of the wide-gap semiconductor n-GaN layer 13 but are formed.
Based on the impedance under a monochromatic light irradiation environment of a predetermined wavelength after application of a pulse voltage, the deep level and valence band information can be determined by the correspondence between the wavelength of the emitted monochromatic light and the rate of change in capacitance or conductance. It is possible to obtain a transient response characteristic of capacitance or conductance in accordance with optical excitation such as, and to perform band gap electronic property measurement such as deep level and valence band information of the wide gap semiconductor n-GaN film 13 with high sensitivity. .
Since the work function of the organic metal film 15 is larger than that of the noble metal, the band gap electronic property measurement is possible even in a wide gap semiconductor having a high carrier concentration of about 1 × 10 ¹⁸ cm ⁻³ . Thereby, the band structure analysis of a wide gap semiconductor within a wide carrier concentration range of 1 × 10 ¹⁶ to 1 × 10 ¹⁸ cm ⁻³ becomes possible. Since it is possible to measure a high carrier concentration, it is possible to detect the band gap physical property information of the semiconductor surface portion, which was difficult to measure with the prior art.
In order to perform measurement by irradiating the monochromatic light from the organic metal film 15 side by the monochromatic light irradiation unit 23,
Electrical property measurement of various wide-gap semiconductors grown on a substrate such as Si that does not transmit light is possible, and it can be applied to various semiconductors regardless of the substrate type.

When the organic metal film 15 is formed of polyaniline, as shown in FIG. 7, the capacitance rapidly decreases in the vicinity of 10 kHz (10 ⁴ Hz), the admittance has a peak, and the cutoff frequency is 10 kHz.
In order to avoid the influence of dielectric dispersion, it is preferable to set the impedance measurement frequency to be equal to or higher than the cutoff frequency of the organic metal film 15. For example, when the organometallic film 15 is formed of polyaniline, the impedance measurement frequency is preferably 10 kHz or more.

FIG. 8 shows the measurement frequency dependence of the spectrum of the relationship between the incident light energy (eV) and the change amount of the photocapacitance ΔC _SS / C ₀ . Here, the capacitance _{C 0,} the reference state (and the dark state, non-charge injection state) is the value at, 2N _D [Delta] C _SS / _{C 0} shows a defect level density (cm ^-3). The measurement frequency was three levels of 1, 10, and 100 kHz. The voltage pulse for carrier injection was set to a pulse voltage of 0 V and a pulse width of 1.0 s. The measurement voltage was −2V.

Compared to the measurement frequencies of 1 and 10 kHz, the band gap electronic properties were remarkably observed at the measurement frequency of 100 kHz. Here, the T1, T2, and T3 levels that are peculiar defect levels of n-GaN, the G1, G2 levels that are detected at the AlGaN / GaN hetero interface, and the valence band information of n-GaN. A certain NBE (Near Band Edge) was detected.
In this way, the capacitance change rate is measured by changing the measurement frequency of the impedance, and by measuring the measurement frequency dependence, the measurement frequency at which the level information in the band gap is appropriately obtained is set, and the high carrier concentration It was confirmed that the level information in the band gap of the n-GaN film 13 can be evaluated.

FIG. 9 shows the measured voltage dependence of the spectrum of the relationship between the incident light energy and the amount of change in capacitance. Here, the measurement voltage was set to three levels of -2, -5, and -8V. The voltage pulse for carrier injection was 0 V, the pulse width was 1.0 s, and the impedance measurement frequency was 100 kHz. The measurement voltage −2V corresponds to the measurement depth range 42 to 70 nm from the surface of the n-GaN film 13, the measurement voltage −5V corresponds to the measurement depth range 42 to 98nm, and the measurement voltage −8V corresponds to the measurement depth range 42 to 120nm. .

It was recognized that the level density of G1 and T3 increased as the measurement voltage was in the order of −8, −5, −2V, that is, the measurement depth range became shallower. Since the G1 level and the T3 level are densely distributed in the GaN surface layer, it was found that the band gap level of the surface layer can also be measured. As a result, the change rate of capacitance is measured by changing the measurement voltage, and by measuring the measurement voltage dependence, a measurement voltage that appropriately obtains the band gap level information of the surface layer is set, and the band gap of the surface layer is set. It was confirmed that the level information can be evaluated.

(Example of change)
The wide gap semiconductor to which the evaluation method of the present invention can be preferably used is not limited to GaN, but preferably a semiconductor that forms an organic metal film and a high Schottky barrier exceeding 1.2 eV, for example. be able to. Examples thereof include nitride semiconductors such as AlN, BN, and AlGaN, oxide semiconductors such as ZnO, SnO ₂ , and TiO _2, and carbide semiconductors such as diamond and SiC. Further, any of p-type and n-type semiconductors may be used.

The organic metal film 15 is not limited to ponianiline as long as it can form a Schottky junction with a wide gap semiconductor. For example, polyacetylene, polyphenylene, poly (3,4-ethylenedioxythiophene) -poly (styrenesulfone) is used. Acid), poly (3,4-ethylenedioxythiophene) -poly (ethylene glycol) block copolymer and other conductive organic materials, particularly hole-conducting organic materials can be suitably used.

[Effect of the embodiment]
(1) According to the band gap electronic property measurement method of a wide gap semiconductor of the present invention, the surface of the n-GaN film 13 which is a wide gap semiconductor has translucency capable of forming a Schottky junction with the wide gap semiconductor. Through the Schottky electrode forming process for forming the organometallic film, the conductive organometallic film 15 having a wide band gap and a large work function is formed as a wide-gap semiconductor Schottky electrode, and the monochromatic light irradiation unit 23 Thus, as the monochromatic light, for example, monochromatic light with sufficiently high wavelength resolution is spectrally irradiated from the metal organic film 15 side, and the wide-gap semiconductor n-GaN film 13 in which the metal organic film 15 is formed by the voltage pulse generation unit 21. A pulse voltage having a predetermined voltage intensity is applied to the electrode at a predetermined timing, and the organic gold is measured by the impedance measuring unit 22. It is possible to detect the impedance of the wide-gap semiconductor n-GaN film 13 film 15 is formed.
Based on the impedance under a monochromatic light irradiation environment of a predetermined wavelength after application of a pulse voltage, the deep level and valence band information can be determined by the correspondence between the wavelength of the emitted monochromatic light and the rate of change in capacitance or conductance. It is possible to obtain a transient response characteristic of capacitance or conductance in accordance with optical excitation such as, and to perform band gap electronic property measurement such as deep level and valence band information of the wide gap semiconductor n-GaN film 13 with high sensitivity. .
Since the work function of the organic metal film 15 is larger than that of the noble metal, the band gap electronic property measurement is possible even in a wide gap semiconductor having a high carrier concentration of about 1 × 10 ¹⁸ cm ⁻³ . Thereby, the band structure analysis of a wide gap semiconductor within a wide carrier concentration range of 1 × 10 ¹⁶ to 1 × 10 ¹⁸ cm ⁻³ becomes possible. Since it is possible to measure a high carrier concentration, it is possible to detect the band gap electronic property information of the semiconductor surface portion, which was difficult to measure with the conventional technology.
Since the monochromatic light irradiation unit 23 irradiates the monochromatic light from the side of the organic metal film 15 and performs the measurement, it is possible to measure the electronic properties of various wide gap semiconductors grown on a substrate that does not transmit light such as Si. It can be applied to various semiconductors regardless of the substrate type.

(2) By setting the impedance measurement frequency to a frequency equal to or higher than the cutoff frequency of the organic metal film, the influence of dielectric dispersion can be avoided and the measurement accuracy can be improved.

(3) The capacitance change rate is measured by changing the impedance measurement frequency, and the measurement frequency dependence is examined to set the measurement frequency at which band-band level information can be appropriately obtained. Information can be evaluated.

(4) The capacitance change rate is measured by changing the measurement voltage, and the measurement voltage dependency is examined to set a measurement voltage at which the band gap level information of the surface layer can be appropriately obtained. Level information can be evaluated.

1 ... Evaluation sample,
2 ... Evaluation device,
11 ... c-Al ₂ O ₃ substrate,
12 ... ud-GaN film,
13 ... n-GaN film,
14 ... Metal electrode,
15 ... Organic metal film,
21 ... Voltage pulse generator (voltage pulse generator),
22: Impedance measuring section (impedance measuring means),
23: Monochromatic light irradiation unit (monochromatic light irradiation means),
24 ... control unit,
25. Measurement control unit,
26. Calculation unit

Claims (4)

A band gap electronic property measurement method for a wide gap semiconductor,
A step of forming a Schottky electrode on the surface of the wide gap semiconductor to form a translucent organometallic film capable of Schottky junction with the wide gap semiconductor;
The monochromatic light irradiation means irradiates the wide gap semiconductor on which the organometallic film is formed with monochromatic light having a predetermined wavelength from the organometallic film side at a predetermined timing and intensity,
By applying a pulse voltage having a predetermined voltage intensity at a predetermined timing to the wide gap semiconductor on which the organometallic film is formed by the voltage pulse generating means,
The impedance measurement means detects the impedance of the wide gap semiconductor on which the organometallic film is formed,
Based on the impedance under a monochromatic light irradiation environment of a predetermined wavelength after application of the pulse voltage,
A band gap electronic property of the wide gap semiconductor is evaluated based on a correspondence relationship between the wavelength of the irradiated monochromatic light and the capacitance or conductance change rate of an electron depletion layer formed immediately below the Schottky electrode. Band gap electronic property measurement method of gap semiconductor. The method of measuring a band gap electronic property of a wide gap semiconductor according to claim 1, wherein the measurement frequency of the impedance is set to a frequency equal to or higher than a cutoff frequency of the organometallic film. When the change rate of the capacitance is used to evaluate the band gap electronic properties of the wide gap semiconductor, the change rate of the capacitance is measured by changing the measurement frequency of the impedance, and the measurement condition is set based on the measurement frequency dependency. The band gap electronic property measurement method for a wide gap semiconductor according to claim 1, wherein the in-band gap level information is evaluated. When the change rate of the capacitance is used for evaluating the band gap electronic physical properties of the wide gap semiconductor, the change rate of the capacitance is measured by changing the measurement voltage, the measurement condition is set based on the measurement voltage dependency, and the surface 3. The band gap electronic property measurement method for a wide gap semiconductor according to claim 1, wherein band gap level information of the layer is evaluated.

Images